The use of integrated or detachable wheels to facilitate the movement of luggage is well known. Usually, these wheels are located on a side or end of a suitcase, either a single pair of wheels or as multiple wheels.
U.S. Pat. No. 5,407,039 discloses wheeled luggage that is self stabilized and towable via a rigid handle. Here, non-swiveling wheels are placed on an edge of a suitcase and one or more swiveling wheels are placed in the underside of the suitcase. This approach yields a more stable suitcase, which allows a child seat to be fixed to the top of the suitcase.
Stackable storage containers are well known and have been used in conjunction with wheeled carts or dollies.
U.S. Pat. No. 3,532,355 discloses a luggage carrier that can be temporarily attached to a base suitcase of a stack of suitcases to allow the base suitcase to be used as a dolly. However, the stack of suitcases may become unstable when sliding forces are present. This occurs when a corner is turned or when a slope is encountered, for example.
This instability problem is made worse when a stacked item has a cylindrical or spherical shape that tends to roll. Examples include balls for soccer or other sports, cylindrical bags for carrying golf clubs, tubes for carrying art work, and air cylinders for scuba diving.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.